diff --git a/src/os2/slider.cpp b/src/os2/slider.cpp
index 0a6eb8f985..312d9743c9 100644
--- a/src/os2/slider.cpp
+++ b/src/os2/slider.cpp
@@ -863,8 +863,10 @@ void wxSlider::GetSize(
         wxFindMaxSize( m_hStaticValue
                       ,&vRect
                      );
-    *pnWidth  = vRect.xRight - vRect.xLeft;
-    *pnHeight = vRect.yBottom - vRect.yTop;
+    if (pnWidth)
+        *pnWidth  = vRect.xRight - vRect.xLeft;
+    if (pnHeight)
+        *pnHeight = vRect.yTop - vRect.yBottom;
 } // end of wxSlider::GetSize
 
 int wxSlider::GetThumbLength() const